In order to provide improved appearance, longer life, and increased reliability for metal based consumer and industrial products, it has become an accepted practice to conversion coat metallic surfaces prior to the application of a paint, lacquer, or oil. The conversion coated metallic surface is in turn treated with a post-treatment to impart further humidity and corrosion resistance thereto. The treatment or final rinse frequently is a chromium containing composition such as described in U.S. Pat. Nos. 3,222,226, and 2,970,935. The use of heavy metals such as chromium in metal treating lines may result in pollution.
Many chromium containing compositions have further side effects of leading to blistering of the final organic film under conditions of high humidity at areas where the posttreatment solution can concentrate before drying. One method of overcoming this problem is to water rinse (preferably with deionized water) the work before painting. This is especially desirable before electropainting where the paints are water based and soluble contaminants can unbalance the paint. Many chromium containing post-treatments wash off in this water rinse thus losing their ability to inhibit paint loss due to under paint corrosion.
Therefore, a post-treatment which will eliminate heavy metal ions such as chromium, and which will also allow water rinsing without decrease in corrosion resistance is desirable.